同(tong)(tong)心(xin)異(yi)徑(jing)管(guan)(guan)(guan)又叫同(tong)(tong)心(xin)大小(xiao)頭尺(chi)寸允許偏差應符合(he)表4.2.2-3的規定.異(yi)徑(jing)管(guan)(guan)(guan)也叫大小(xiao)頭,用(yong)來連接不同(tong)(tong)尺(chi)寸的管(guan)(guan)(guan)子,一般它(ta)分為同(tong)(tong)心(xin)異(yi)徑(jing)管(guan)(guan)(guan)和(he)偏心(xin)異(yi)徑(jing)管(guan)(guan)(guan)兩種,當異(yi)徑(jing)管(guan)(guan)(guan)立起來后兩端口(kou)的投影是(shi)同(tong)(tong)心(xin)圓(yuan)時,它(ta)就叫同(tong)(tong)心(xin)異(yi)徑(jing)管(guan)(guan)(guan),而偏心(xin)異(yi)徑(jing)管(guan)(guan)(guan)的投影是(shi)小(xiao)圓(yuan)內切于外(wai)圓(yuan).

同(tong)(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)(xin)異(yi)(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)的(de)(de)制(zhi)造工(gong)藝(yi)(yi)簡(jian)單，用(yong)壁(bi)(bi)厚較(jiao)厚的(de)(de)管(guan)(guan)(guan)(guan)(guan)(guan)作為(wei)(wei)(wei)毛坯，擴大(da)一(yi)端(duan)口(kou)(kou)(kou)(kou)(kou)徑(jing)(jing)(jing)(jing)(jing)(jing)或者用(yong)等壁(bi)(bi)厚的(de)(de)管(guan)(guan)(guan)(guan)(guan)(guan)作為(wei)(wei)(wei)毛坯，縮小一(yi)端(duan)口(kou)(kou)(kou)(kou)(kou)徑(jing)(jing)(jing)(jing)(jing)(jing)均(jun)可。無(wu)論擴口(kou)(kou)(kou)(kou)(kou)或縮口(kou)(kou)(kou)(kou)(kou)，一(yi)般是用(yong)模具壓(ya)制(zhi)。當前國內(nei)(nei)(nei)普遍采用(yong)偏(pian)(pian)(pian)心(xin)(xin)(xin)(xin)(xin)(xin)模具逐級壓(ya)制(zhi)偏(pian)(pian)(pian)心(xin)(xin)(xin)(xin)(xin)(xin)異(yi)(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)，用(yong)這種工(gong)藝(yi)(yi)生產的(de)(de)三級以上的(de)(de)偏(pian)(pian)(pian)心(xin)(xin)(xin)(xin)(xin)(xin)異(yi)(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)，在(zai)(zai)小頭偏(pian)(pian)(pian)心(xin)(xin)(xin)(xin)(xin)(xin)端(duan)會(hui)產生嚴重(zhong)缺口(kou)(kou)(kou)(kou)(kou)、內(nei)(nei)(nei)壁(bi)(bi)起(qi)瘤、壁(bi)(bi)厚不均(jun)勻及橢圓(yuan)等現(xian)象。按斜截同(tong)(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)(xin)異(yi)(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)截頭所得(de)結(jie)構代替偏(pian)(pian)(pian)心(xin)(xin)(xin)(xin)(xin)(xin)異(yi)(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)時，因為(wei)(wei)(wei)斜截面(mian)不是圓(yuan)面(mian)而是橢圓(yuan)面(mian)，就(jiu)會(hui)存在(zai)(zai)端(duan)面(mian)與(yu)直管(guan)(guan)(guan)(guan)(guan)(guan)之間(jian)的(de)(de)錯邊、無(wu)法完全相(xiang)接的(de)(de)問題。如果采用(yong)新的(de)(de)壓(ya)制(zhi)工(gong)藝(yi)(yi)，即先用(yong)同(tong)(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)(xin)模具壓(ya)制(zhi)出同(tong)(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)(xin)異(yi)(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)，再把壓(ya)好的(de)(de)同(tong)(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)(xin)異(yi)(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)放入偏(pian)(pian)(pian)心(xin)(xin)(xin)(xin)(xin)(xin)模具中壓(ya)制(zhi)整(zheng)型為(wei)(wei)(wei)所需要的(de)(de)偏(pian)(pian)(pian)心(xin)(xin)(xin)(xin)(xin)(xin)異(yi)(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)，則其內(nei)(nei)(nei)、外表面(mian)光滑(hua)，小頭平整(zheng)，壁(bi)(bi)厚均(jun)勻，圓(yuan)度(du)合格，所用(yong)原材料較(jiao)少。同(tong)(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)(xin)異(yi)(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)的(de)(de)質量應符合現(xian)行(xing)標(biao)準《鋼制(zhi)對焊(han)無(wu)縫管(guan)(guan)(guan)(guan)(guan)(guan)件》GB/T 12459-2005的(de)(de)規(gui)定,并應滿(man)足下列要求:1) 同(tong)(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)(xin)異(yi)(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)的(de)(de)圓(yuan)度(du)不應大(da)于(yu)相(xiang)應端(duan)外徑(jing)(jing)(jing)(jing)(jing)(jing)的(de)(de)1%,且允許偏(pian)(pian)(pian)差為(wei)(wei)(wei)±3mm,同(tong)(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)(xin)異(yi)(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)兩端(duan)中心(xin)(xin)(xin)(xin)(xin)(xin)線(xian)應重(zhong)合,其偏(pian)(pian)(pian)心(xin)(xin)(xin)(xin)(xin)(xin)值允許偏(pian)(pian)(pian)差為(wei)(wei)(wei)±5mm.2) 同(tong)(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)(xin)異(yi)(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)外觀不應有裂(lie)紋,重(zhong)皮,壁(bi)(bi)厚應大(da)于(yu)大(da)徑(jing)(jing)(jing)(jing)(jing)(jing)端(duan)管(guan)(guan)(guan)(guan)(guan)(guan)段的(de)(de)壁(bi)(bi)厚.12459-2005里面(mian)同(tong)(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)(xin)異(yi)(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)標(biao)準允許偏(pian)(pian)(pian)差DN15-65 口(kou)(kou)(kou)(kou)(kou)徑(jing)(jing)(jing)(jing)(jing)(jing)：+1.6 -0.8 內(nei)(nei)(nei)徑(jing)(jing)(jing)(jing)(jing)(jing)：±0.8 高度(du)： ±2DN80-100 口(kou)(kou)(kou)(kou)(kou)徑(jing)(jing)(jing)(jing)(jing)(jing)：±1.6 內(nei)(nei)(nei)徑(jing)(jing)(jing)(jing)(jing)(jing)：±1.6 高度(du)： ±2DN125-200 口(kou)(kou)(kou)(kou)(kou)徑(jing)(jing)(jing)(jing)(jing)(jing)：+2.4 -1.6 內(nei)(nei)(nei)徑(jing)(jing)(jing)(jing)(jing)(jing)：±1.6 高度(du)： ±2DN250-450 口(kou)(kou)(kou)(kou)(kou)徑(jing)(jing)(jing)(jing)(jing)(jing)：+4 -3.2 內(nei)(nei)(nei)徑(jing)(jing)(jing)(jing)(jing)(jing)：±3.2 高度(du)： ±2DN500-800 口(kou)(kou)(kou)(kou)(kou)徑(jing)(jing)(jing)(jing)(jing)(jing)：+6.4 -4.8 內(nei)(nei)(nei)徑(jing)(jing)(jing)(jing)(jing)(jing)：±4.8 高度(du)：DN500-600 ±2 DN650-750 ±3 DN800 ±5壁(bi)(bi)厚不小于(yu)公(gong)稱壁(bi)(bi)厚的(de)(de)87.5%圓(yuan)度(du)偏(pian)(pian)(pian)差為(wei)(wei)(wei)正負值之和(he)。但是一(yi)般500以下圓(yuan)度(du)為(wei)(wei)(wei)4MM以內(nei)(nei)(nei)。